Sweetening hydrocarbon mixtures



Patented Mar. 6, 1951 Elwood 'B...Backensto, Woodbury,

N. J., assignor .to Socony-Vacuum Oil Company, Incorporated, a corporation of New York NoJDrawing. Application November 21, 1947,

serialtNo. 787,483

'13 Claims. 196-29) The present invention relates to ,the sweetening of hydrocarbon mixtures -,and, more particularly, to the sweetening of ,petroleumidistillates.

sweetening may be broadly definedas an-operation inwhich the concentration of the organic sulfur compounds in .a hydrocarbon ,mixture .is reduced to a value such .that the doctor test is negative.

A hydrocarbon. mixture containing. sulfhyd i ls is said-to .be sourj. orto bepositivein the common doctor test, if it contains more than about 0.0004 per cent sulf-ur calculated as mercaptan and .isfreefrom hydrogensulfidait is said to be fsweet or to be negative in the "doctor test when the sulfur concentration is below that-value.

The doctor test comprises addin cubic centimeters of the oil to be tested to 5 cubic centimeters of'sodium plumbitesolution (made by dissolving 120 to 140 grams of sodium hydroxide and 20.to 30 grams of litharge inaliter of water) in a standard testbottle (4 ounce sample bottle, 33 millimeters inside diameter,=fitted with a clean cork stopper). The bottleisstoppered, shaken for seconds, and dry fiowers of sulfur (ground and screened to 100 to 200 mesh) added to the mixture in quantity just sufficient to cover the interface to x3-5emiliigrams). The bottle is again stoppered and shaken for ,15 seconds. ,The test is reported positive if either the oil or the sulfur becomes discolored.

The minimum amount of mercaptan sulfur required to give a positive doctor test in a sample of Stoddard c1eanerssolvent is shown in Table I.

Table I Minimum per cent by weight of mercaptan sulfur in naptha required to give Positive Doctor qTest Mereaptan Since hydrocarbonrmixtures usually contain two or more mercaptans and since the distribution of the mercaptansin hydrocarbon: mixtures is not constant, a practical value for themaximum per cent by weight "of"mercapta"n*sulfur"-"-which will .2 giveanegativedoctor test is usually accepted-as 0.0004 per cent.

Mixture .of hydrocarbons containing sulfhydryls canbe treated in accordance with several procedures to produce 2. treated mixture which is negative to the doctor test. However, all of these procedures do ,not produce the same re-.

sult. .For example, the so-called doctor sweetening .and the copper .chloride sweetening methods merely convert sufiicient of the mercaptans present in the hydrocarbon mixture to disulfides that the treated. mixture is negative in the doctor test. ethylJeadis not to be added the presence of the disulfides is notiobjectionable. Onthe other hand, thepresence of disulfides in gasoline .to

whichtetraethyllead is to be added is objectionable because the presenceof disulfides reduces the sensitivity of thegasoline to the addition of the lead to even a greater extent than a corresponding .concentration of mercaptans. Since mostgasolines now marketed are treated with tetraethylleadit follows that it is most desirablev to remove the mercaptans rather than merely convertthem to disulfides. As a consequence, the removal of .mercaptans has become desirable. To meet this demand, methods have been devised which make it possible to remove substantially all'of'the mercaptans. However, while it is usu-. ally relatively easy to reduce the mercaptan sul-,

fur content of cracked and straight run gasoline to a value of the order of 0.0007 to 0,003 per .cent

sulfur as mercaptan sulfur by treatment with the"well-knownsolutizer solutions such as aque-' ous caustic-tannin .and. aqueous caustic cresylatetannin solution or other caustic-solutizer solutions, the reduction of the mercaptan-sulfur contentof gasoline from 0.0007 or 0.003 to 0,0004 not accomplished as readily, On the other hand, gasoline containing 0.0007 to 0.003 per cent mer captan sulfur is not doctor, sweet.

It hasnow been discovered that sour, hydroe, carbonmixtures containing organic su1fhydryls canbetreated in a simple,inexpensive but efli cacious manner toprovide a doctor sweet? mixture.

It is an object of the present invention to pro-,-

videgamethodfor sweetening" sour hydrocarbon mixtures. ,It isanother object of present invention to provide a. method for removing a portion of the mercaptan content of a sour,hydrocarbon mixture and, then to sweet- -th p t l emer antamz d, but o h rocarbon nixture ,lti 'afurth objec of he. ,present invention to add a hydrocarbon soluble For gasoline to which ,tetra sweetening agent to hydrocarbon mixtures containing not more than about 0.02 weight per cent sulfur as organic sulfhydryls to produce a hydrocarbon mixture negative to the doctor test. Other objects and advantages will become apparent from the following description.

Two conditions, in general, will be met in the treatment of sour mixtures of hydrocarbons. The sour mixture may contain only about 0.005 weight per cent mercaptan sulfur or the sour mixture may contain appreciably more than about 0.005 weight per cent mercaptan sulfur.

For the purpose of illustrating the present method, the treatment of sour gasoline containing not more than about 0.005 weight per cent mercaptan sulfur (including alkyl and aryl mercaptans, the latter often being termed thiophenols) first will be described. When the gasoline contains hydrogen sulfide as well as not more than about 0.005 weight per cent mercaptan sulfur, the hydrogen sulfide is removed in a conventional manner by washing the gasoline with an aqueous caustic solution. This caustic wash removes the hydrogen sulfide and a portion of the C1 and C2 mercaptans. However, the gasoline will still be positive in the doctor test. The washed gasoline also contains a small amount of alkali metal hydroxide. The sour caustic washed gasoline containing not more than about 0.005 weight per cent mercaptan sulfur is sweetened by adding a small amount of a sweetening agent and the sweetening agent allowed to react with the mercaptans. After about 30 minutes to about '7 days at ambient temperatures, dependent upon the concentration of the sweetening agent, the so-treated gasoline is negative to the doctor test. When it is unnecessary to wash the gasoline with an aqueous solution of alkali metal hydroxide, it is necessary to add a trace, say about 0.001 pound to about 0.02 pound of alkali metal hydroxide per barrel of gasoline.

Illustrative of the treatment of a sour mixture of hydrocarbons containing appreciably more than 0.005 weight per cent of mercaptan sulfur, is that of a sour gasoline containing say 0.03 weight per cent mercaptan sulfur but free from hydrogen sulfide. Such a gasoline is contacted with an aqueous solution of alkali metal hydroxide or an aqueous solution of alkali metal hydroxide containing a solutizer. Illustrative of such solutions are the commonly used sodium hye droxide-sodium cresylate solution which is 5.0 normal to sodium hydroxide and 2.0 normal sodium alkyl phenolates; or the well know aqueous solutions of potassium hydroxide and potassium alkyl phenolates, or an aqueous sodium hydroxide-sodium cresylate solution containing a polyhydroxy benzene or a polyhydroxy benzene carboxylic acid or a tannin or an aqueous potassium hydroxide-potassium cresylate-tannin solution or; in general, any of the aqueous alkaline solutizer solutions described in the voluminous literature on this subject and known to those skilled in the art may be used. The "sour gasoline is treated with the aqueous alkaline solution until sufficient of the mercaptans have been extracted from the sour gasoline that although the treated gasoline is still positive in the doctor test it does not contain more than about 0.02 and preferably less than about 0.005 weight per cent mercaptan sulfur. The partially demercantanized "sour gasoline containing not more' than about 0.02 weight per cent mercaptan sulfur is separated from the aoueous treatin solution and sweetened by adding thereto a sweetening agent. The gas'o-' line and added sweetening agent are reacted for a period of time dependent upon the temperature and concentration of the sweetening agent.

The preferred sweetening agent at this time is di-secondary butyl catechol. This catechol and several other compounds have been added to sweetened gasoline, i. e. gasoline negative in the doctor test in the past to inhibit the formation of gum during storage. However, the present method of sweetening sour mixtures of hydrocarbons distinguishes from this prior use of di-secondary butyl catechol. In the prior use of this catechol and other gum inhibitors the gum inhibitor was always added to sweet gasoline which was negative in the doctor test, i. e. contained less than 0.0004 weight per cent of mercaptan sulfur. In the prior use of these gum inhibitors the sweet gasoline did not contain a trace of caustic. In contrast to the conditions attendant upon the prior use of alkyl catechols and other compounds in the inhibition of the formation of gum in sweet neutral gasoline, the alkyl catechols are employed under the following conditions: The gasoline is sour, i. e. positive in the doctor test and the gasoline contains at least a trace of alkali metal hydroxide and is probably saturated with water. Furthermore, all of the prior-art gum inhibitors are not effective in the present method of sweetening gasoline. This is established in the following tables.

Table II Days at ambient temperature to sweeten gasoline Additive lbs./l000 bbl. containingObOSwt.

' mercaptan and alkali metal hydroxide None l2 Di-seeondary butyl catechol.. 20 less than 1 Di-secondary butyl phenylene diamine 20 5 Trialkyl phenols 20 15 Normal butyl amino phen 20 17 Alpha-naphthol 20 14 Quinone 20 5 Catcchol 20 more than 19 Table III Days at ambient ag gis fib temperatures to Alkali metal hydroxide er 1000 bbls sweeten gasoline p gasoline containing 0.005 wt. mercaptan sulfur present 0 42 D l0 7 0 42 10 42 Table IV Lbs. alkyl catechol per 1000 bbls. of gasoline containing alsweeten; i. e. give a kali metal hydroxnegative doctor ide and 0.005 wt. test mercaptan sulfur Days at ambient temperatures to O 13 0.25 7 0. 5O 7 0.75 6 l. 0 4 2- 0 3 3. 0 2 4. 0 0. 83 5. 0 0. 13 10. 0 0. 04 20. 0 0. O2

ear-scenes alkyl oatechols .are far superior in the ipresent.

method of sweetening sour hydrocarbon mixtures containing about 0.005 weight per cent mercaptan sulfur. catechol establishes that unsubstituted catechol is ineffective, if it 'does not actually :retard; in sweetening :of sour gasoline containing 0.005 weight per cent mercaptansulfur.

The data presented in "Table III establishes that in the absence of alkali metal hydroxide even di-secondary 'butyl catechol: at v a. concentration of -10 pounds per 1000 barrels of gasoline is ineffective -to :s-weeten sour gasoline containing abouto05 weight per cent mercaptan sulfur but that in the presence of *alkali metal hydroxide di secondary 'butyl catechol is effective in sweetening 'sour gasoline containing about"0.005 weight per cent of mercaptan sulfur.

The-data presented in "Table IV establishes that in the presence of alkali metal hydroxide the ratecf sweetening sour gasoline containing about 0.005 weight per cent mercaptansulfur is dependent upon the concentration of alkyl catechol. A study of the data given inTable'IV makesit manifest that-the amount ofal-kyl catechol to be -used in sweeteningsour hydrocarbon mixtures containing not more than 0:02 weight per cent mercaptan sulfur will depend to a great extent upon local conditions-primarily local economic conditions. Thus, when a large volume of storage is-available for 'a-week at a time and the capacity exceeds the demand, it probably will be-m0st'-practica1 -t0 use about 0.25 pounds of alkyl catechol ,per 100 barrels in treating gasoline containing about 0.005 weight per cent mercaptansulfu-r and. allow-the reaction to proceed for several days at ambientxtemperatures. On the other -.hand, when sufiicient storage capacity is not available or demand is practically equal tothe capacity to produce the sour gasoline, it will probably'be most "practical to add about 4 to about 20 pounds of alkyl catechol per 1000 barrels of sour lhydrocarbon'mixture and allow the reaction to proceed atambient temperatures orto usesomewhat less,.say 2 to,5.,poun.ds, alkyl catechol and reflux the sour gasoline and alkyl catechol in the presence of a small amount of alkali ,metal hydroxide.

Furthermore, when Storage capacity, production and consumption justif y such procedure .it is possible to sweeten gasoline and other mixtures of hydrocarbons such as kerosene, Diesel oil, and heating oil containing up to 0.02 weight per cent of mercaptan sulfur without first subjecting the mixture hydrocarbons to an operation for partially de-mercaptanizing the hydrocarbon mixture under such conditions larger amounts. say 3 to 5 times, of the predetermined additive and larger amounts of caustic can be added to the mixture of hydrocarbons and the mixture of hydrocarbons, sweetening additive, and caustic allowed to react for a longer period of time, say up to three or four times that required to sweeten a similar mixture of hydrocarbons containing about 0.005 weight per cent mercaptan sulfur.

The general procedure can be modified further with improved results. That is the rate of sweetening can be accelerated by adding the sweetening additive or agent before subjecting the mixture of hydrocarbons to a caustic wash. The data submitted in Table Vis a basis for the foregoing statement.

he data presented "for.

ydrocarbon mixture sul ur.

Sweeteningadditivepragent di-secondary butyl catechol.

Goncentration of sweeteningeadditive or agent :5 and '10 mounds; pen-100.0, barrels.

: V ,Sweetening'time, Weighijfi .hours' Q Inercap ansegue lcggg a i l iitmn 0i isvulfm t v untreatedf '5 pounds 10 pounds .:gasoline 1 per-1000 v penlODO bbls. .bbls.

1- aQ-asolinerl-sweetening. I "agent-{ 10% wash of aque-' i one 20%;=KOH 204005? .0 50 2, Gas o1-ine,+10% .rwiash .-.of

aqueous 20% 'K'OH+ l -ssweetening.-agent 0.005 F3 11 3 .Gasoline-l-Swecten-ing agent-F30 parts per million of 3% alcoholic KOH; '0. 007' 20 4 Gasoline+sodinm :salt ,of:

sweetening agent 0. 005 I 1 Practically instantaneous.

Mixture ofhydrocarbons-z gasoline.

Mercaptamsulfur content, weight peryzcent .merceptan- .snlfur :..0.0Q5.

Pounds 'of iii-secondary*butyl-catechql per 1000 barrels of gasoline: 5.

Sequence of addition of reagents: .gasol1ne plus sweeten- -ing agent-plus "contact with aqueous 20% KOH.

' -Sweet- Condition ening time Hours Air Present" l 2 A rr x lu d -T ,-g- 9 Accordingly, the present inventiongccmprises eeteni asg m tu e o hy ocarb in n no mor than ab u .0-0 .pe :cent and preferably less than about 0.005 per .cent :by weight of mercaptan-sulfur'by the action of a gum inhibitor selected from the group consisting of alkyl catechols, alkaryl diamines and quinones in the presence of alkali metal hydroxide. Preferably, the sweetening agent, i. e. the gum inhibitor, is added to the sour mixture of mercaptans before the mixture of hydrocarbons is contacted with air and aqueous solution of alkali metal hydroxide. In addition, it is preferred to sweeten the sour mixture of hydrocarbons in the presence of a gas containing free oxygen.

I claim:

1. A method of producing a petroleum fraction negative in the doctor test from a sour pe troleum fraction containing not more than about 0.02 weight per cent of mercaptan sulfur which comprises mixing a sour petroleum fraction containing not more than about 0.02 weight per cent mercaptan sulfur with a di-secondary butyl catechol in the presence of alkalimetalihydroxide.

v I g V jtannin-sclutizcr"treated gasoline con taming'rorfl05 -it0 #01007 :weig'ht eper -.-cent mercaptan- 2. The method described and set forth in claim 1 in which the sour petroleum fraction and disecondary butyl catechol are maintained at ambient temperatures.

3. The method described and set forth in claim 1 in which the sour petroleum fraction and disecondary butyl catechol are maintained at a temperature between ambient temperatures and the reflux temperature.

4. A method of sweetening a sour petroleum fraction which comprises partially demercaptanizing a sour petroleum fraction to obtain a treated petroleum fraction positive in the doctor test and containing not more than about 0.005 weight per cent mercaptan sulfur, separating said treated petroleum fraction from the treating medium and, mixing said treated petroleum fraction with a di-secondary butyl catechol in the pres ence of alkali metal hydroxide.

5. The method described in claim 4 in which the mixture of treated petroleum fraction and di-secondary butyl catechol is maintained at ambient temperatures.

6. The method described in claim 4 in which the mixture of treated petroleum fraction and di-secondary butyl catechol is heated to reflux in the presence of alkali metal hydroxide.

'7. A method of sweetening a sour petroleum fraction which comprises contacting a sour petroleum fraction with an alkaline solutizer solution containing a tannin to demercaptaniz partially said fraction and provide a treated fraction positive in the doctor test and containing not more than about 0.005 weight per cent mercaptan sulfur, separating said treated fraction from said alkaline solutizer solution, and mixing said treated fraction with di-secondary butyl catechol.

8. The method as set forth in claim '7 in which the butyl catechol and treated gasoline are heated to reflux temperatures.

9. A method of sweetening a sour petroleum fraction which comprises contacting a sour petroleum fraction with an alkaline soluti'zer solution'containing a polyhydroxy benzene to demercaptanize partially said fraction and provide a treated fraction positive in the doctor test and containing not more than about 0.005 weight per cent mercaptan sulfur, separating said treated fraction from said alkaline solutizer solution, and mixing said treated fraction with di-secondary butyl catechol.

10. A method of sweetening a sour petroleum fraction which comprises contacting a sour petroleum fraction with an alkaline solutizer solution containing a polyhydroxy benzene carboxylic acid to demercaptanize partially said fraction and provide a treated fraction positive in the doctor test and containing not more than about 0.005 weight per cent mercaptan sulfur, separating said treated fraction from said alkaline solutizer solution, mixing said treated fraction with di-secondary butyl catechol and maintaining the mixture of sour hydrocarbon mixture and alkyl catechol at a temperature between ambient temperature and the reflux temperature.

11. A method of producing mixtures of hydrocarbons negative in the doctor test from sour mixtures of hydrocarbons containing not more than about 0.005 weight per cent mercaptan sulfur which comprises mixing a sour mixture of hydrocarbons containing not more than about 0.005 weight per cent mercaptan sulfur and disecondary butyl catechol in the presence of alkali metal hydroxide.

12. A method of sweetening a sour mixture of hydrocarbons which comprises adding a gum inhibitor selected from the group consisting of disecondary butyl catechol, di-secondary butyl phenylene diamine and quinone to a sour mixture of hydrocarbons containing not more than about 0.02 weight per cent of mercaptan-sulfur, and contacting said mixture of hydrocarbons and said gum inhibitor with an aqueous solution of alkali metal hydroxide.

13. The method described and set forth in claim 12 in which the sweetening of the sour mixture of hydrocarbons is carried out in the presence of a gas containing free oxygen.

ELWOOD B. BACKENSTO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,369,771 Bond Feb. 20, 1945 2,413,945 Bolt Jan. '7, 1947 FOREIGN PATENTS Number Country Date 435,965 Great Britain Oct. 2, 1935 OTHER REFERENCES Bond: Regeneration of Caustic Solutions for Gasoline-Oxidation, reprint from Oil & Gas. Jour., December 8, 1945. 

1. A METHOD OF PRODUCING A PETROLEUM FRACTION NEGATIVE IN THE "DOCTOR TEST" FROM A SOUR PETROLEUM FRACTION CONTAINING NOT MORE THAN ABOUT 0.02 WEIGHT PER CENT OF MERCAPTAN SULFUR WHICH COMPRISES MIXING A SOUR PETROLEUM FRACTION CONTAINING NOT MORE THAN ABOUT 0.02 WEIGHT PER CENT MERCAPTAN SULFUR WITH A DI-SECONDARY BUTYL CATECHOL IN THE PRESENCE OF ALKALI METAL HYDROXIDE. 